The International Telecommunication Union Telecommunication Standardization Sector (ITU-T) existing standards, such as G.8021 and Y.1731, provide latency measurement mechanisms of a transport plane for an Ethernet, and with the mechanisms provided by theses standards, delay values of data frames of the Ethernet which are transmitted in links between two Ethernet devices can be measured. As defined in the G.8051, in order to achieve the object of performance monitoring, an active frame delay measurement needs to collect static statistical data, including a minimum Frame Delay (FD) value, an average FD value, a maximum FD value, a minimum Frame Delay Variation (FDV) value, an average FDV value and a maximum FDV value, and measured values based on each FD value and FDV value are generally collected every other 15 minutes and 24 hours:                Minimum frame delay value and minimum frame delay variation value;        Average frame delay value and average frame delay variation value;        Maximum frame delay value and maximum frame delay variation value.        
On the other hand, in order to achieve the object of maintenance and diagnosis, a latency measurement as required needs to collect certain detailed measured values, and snapshots of the FD and FDV measurement results are collected according to required time intervals (such as 5 minutes or 1 hour).
With respect to an Optical Transmission Network (OTN), the ITU-T existing standard G.709 defines the relevant overhead bytes and latency measurement mechanisms, and with the mechanisms provided by these standards, latency values which occur when signals are transmitted in links between two OTN nodes can be measured. The G.709 adds Path Monitoring (PM)&Tandem Connection Monitoring (TCM) into an overhead byte of an Optical Data Unit (ODU)k, and Path Latency Measurement fields are contained and used for transferring flag bits where the latency measurement starts. The latency measurement can be initiated by a network management or a control plane; a management plane and the control plane also can configure an active measurement way, in which a latency measurement is initiated automatically once every 15 minutes or 24 hours.
A network element performing a latency measurement inserts a Latency Measurement (LMp) flag bit into the overhead byte of the ODUk, and measures the time returning from a “Latency Loopback” network element. When detecting the LMp flag bit, the “Latency Loopback” network element checks the overhead byte of the ODUk, and returns a signal to a “Latency Measurement” network element. A network element initiating the latency measurement must continually check DMp bits received. The “Latency Loopback” network element of the latency measurement must return a latency measurement packet to the network element initiating the latency measurement within a scope of 100 microseconds. The latency measurement must provide an active measurement (every 15 minutes or 24 hours once) or a measurement as required (there is no strict restriction on the time interval). Lengths of two unidirectional ODUk paths in a transmitting direction and a receiving direction may be different, thus the latency of one way is not half of the total latency.
When an Internet Protocol (IP)/Multi-Protocol Label Switching (MPLS) network operates and maintains in a bottom layer circuit switching network (such as a Synchronous Digital Hierarchy (SDH) ring network), a change of the latency in the bottom layer network (due to an action of the network maintenance or an occurrence of a breakdown) cannot be known by the MPLS network. This will cause that the latency influences terminal users, and sometimes a service level agreement subscribed with the clients will be also violated, which leads to user complaints. An alternative solution is to configure the IP/MPLS network in an unprotected circuit switching network and set weights of the links according to latency requirements. This will cause that traffics are oriented to a path with the minimum latency, but actually these paths are not required to satisfy one Service Level Agreement (SLA), and the SLA required by the users may have no need of meeting such a high requirement, thus leading to a reduced flexibility and increased costs. By using the recovering and grooming of the bottom layer network, efficiency can be enhanced, but notifying the IP/MPLS network of performance parameters is not applicable at present. For example, the performance parameters such as the latency and so on are notified to the IP/MPLS network, and thus before the protection and recovering, influence of these parameters on the protection and recovering can be considered.
Signaling protocol message contains Label Switched Path (LSP) parameter information (such as bandwidth, priority establishment and maintenance, and latency and so on). When it is required to allocate an LSP to a member link of complex links, it needs to consider these parameters. When the latency of the member link is changed, it is required to timely notify a client layer. In order to support the latency SLF and provide an operation and maintenance way which can be accepted by the users, the solution should regulate a protocol, which permits the service layer network to notify a top layer client network thereof of the latency.
When the traffics are switched from the current member link to another member link with a different latency, if the latency of a target member link is less than the latency of an original member link, reordering will be performed on the traffics; and when the latency of the target member link is greater than the latency of the original member link, clumping will be performed on the traffics. Therefore, for certain traffics hypersensitive to the influence of latency changes (such as clock synchronization distribution and pseudo wire circuit simulation), it is required to purposely describe the latency requirements in the SLA.
The solution should provide a way, in which that one traffic is indicated to select a member link with an acceptable maximum latency value through the protocol, and meanwhile, one traffic is indicated to select a member link with an acceptable minimum latency value through the protocol.
An unprotected LSP can satisfy SLA requirements of the latency through manual configurations, but this will cause an extremely low usability for optional routes satisfying the SLA requirements of the latency cannot be determined.
Currently, many operators propose network latency test requirements, requiring to provide latency measurements for circuits of the clients in a Dense Wavelength Division Multiplexing (DWDM) transfer system. When network latency measurements are provided for corporate clients who have very high requirements on the latency and for services penetrating optical networks (such as financial affairs and storage services), different latencies can be allocated according to an SLA level. Latency measurement results must be accurate enough to support the SLA, that is, the actual latency must be accurate, and otherwise the services promised to the clients cannot be implemented. However, in the current operation and maintenance mode of the latency measurements, whether latency values of the entire path satisfy the latency requirements of the clients is detected by sending test signals only after determining service routes of the clients, i.e. determining a path in which signals are transmitted. If the latency values do not satisfy the requirements of the clients, it also needs to refind other available routes and perform latency measurement again, and such an operation and maintenance mode has high costs and is extremely time-consuming.
Latency link performance weight information becomes a key demand of the operators, especially with respect to the OTN network, for example, in an overlength transmission system of 100 G, when certain private line services (e.g. an Ethernet Private Line (EPL)) pass through the OTN network, with regard to applications using mirror data based stocks, futures trading and data centers, a subtle latency can influence the trades. Therefore, for those highly value-added clients, the latency and the latency SLF are a key measure for selecting service operators of private line services. Certainly, the lower the latency is, the stronger the competitiveness of the operators in the private line services is, but how to guarantee that the latency after actually opening the services is identical with the latency promised to the clients will also influence the competitiveness of the private line services.